There is known a nonvolatile memory device based on an element with the resistance changing in response to electrical stimulation. This element is subjected to a forming process for applying high voltage to an insulating material provided between electrodes to form a filament constituting a conductive path. However, filaments formed by the forming process are nonuniform, and variations occur in the forming voltage. This may result in destruction of the element during the forming process. Another problem is that the characteristics during the memory operation are unstable.
Patent Document 1 (JP-A 2008-306005) discloses a configuration for filament generation. Structures containing a metal oxide are brought into physical contact with each other along a hole (line) extending from a first electrode to a second electrode. Thus, a filament is generated in this hole and on its extension. However, this method is still insufficient in the controllability for forming a conductive path, and there is room for improvement.